The present invention relates generally to the field of integrated circuit testing and, more particularly, to a method and an apparatus for performing circuit edits in an integrated circuit for the purpose of verifying design engineering change orders.
Once a newly designed integrated circuit has been formed on a semiconductor substrate, the integrated circuit must be thoroughly tested to ensure that the circuit performs as designed. Portions of the integrated circuit that do not function properly are identified so that they can be fixed by correcting the design of the integrated circuit. This process of testing an integrated circuit to identify problems with its design is known as debugging. After debugging the integrated circuit and correcting any problems with its design, the final fully functional integrated circuit designs are used to mass produce the integrated circuits in a manufacturing environment for consumer use. During the debugging process, it is often necessary to add, delete or reroute signal line connections within the integrated circuit.
With continuing efforts in the integrated circuit industry to increase integrated circuit speeds as well device densities, there is a trend towards using flip-chip technology when packaging complex high speed integrated circuits. Flip-chip technology is also known as control collapse chip connection (C4) packaging. In flip-chip packaging technology, the integrated circuit die is flipped upside-down. By flipping the integrated circuit die upside-down, ball bonds may be used to provide direct electrical connections from the bond pads directly to the pins of a flip-chip package.
One consequence of the integrated circuit die being flipped upside-down in a flip-chip package is that access to the internal nodes of integrated circuit die for circuit edit purposes is more difficult. Circuit editing techniques used with wire bond technology are based on performing the circuit edits on metal interconnects through the front side of the integrated circuit die. However, with flip-chip packaging technology, this front side methodology is not feasible since the integrated circuit die is flipped upside-down.
In some cases, a flip-chip may be edited from the back side by thinning down the semiconductor substrate and then trenching down to a point where an edit is desired to be made. A conductive material may be deposited between two locations in order to make a new circuit connection from the back side of the integrated circuit. However, to do so, an insulator is utilized between the conductive connection and the remainder of the circuit. In some cases, an insulator is applied before the conductor is deposited. In other cases, the conductor is only deposited over the field oxide. The provision of an intermediate dielectric layer between the deposited metal and the substrate reduces the overall throughput time of circuit editing. Moreover, the access holes provided to make the connections must be made sufficiently large to accommodate, not only the metal, but also the underlying insulator.
Thus, there is a need for better ways to make circuit edits from the back side of an integrated circuit die.